1. Field of the Invention
The present invention relates to an image forming apparatus including an image forming unit such as an ink jet recording head for forming an image on a sheet of paper, and a platen disposed to face the image forming unit.
2. Description of the Related Art
In an apparatus which ejects ink from nozzles of an ink jet recording head and adheres the ink onto a sheet of paper to form an image on the sheet of paper, a platen is disposed to face a nozzle surface of the recording head, a pair of upstream feed rollers on a feed upstream side (hereinafter merely called “upstream side”) and a pair of downstream feed rollers on a feed downstream side (hereinafter merely called “downstream side”) are disposed so that the platen is put between the pair of upstream feed rollers and the pair of down stream feed rollers. While the two pairs of rollers nip the sheet of paper, the two pairs of rollers are driven intermittently to move (stepwise) the sheet of paper intermittently in a sub-scanning direction. On the other hand, when the intermittent movement is stopped, a carriage equipped with the recording head is moved in a main scanning direction so that images of predetermined sections are one-by-one formed on the sheet of paper supported by the platen.
Incidentally, when ink of the ink jet recording head is put on the sheet of paper, the sheet of paper may be expanded so that cockling of the sheet of paper occurs between the pair of upstream feed rollers and the pair of downstream feed rollers to bring a surface of the sheet of paper into contact with the nozzle surface. As a result, the recorded image is stained with unnecessary ink to reduce image quality. On the other hand, when the sheet of paper curls intensively before the forward end of the sheet of paper to be fed is nipped by the pair of downstream feed rollers or just after the rear end of the sheet of paper is escaped from the pair of upstream feed rollers, the front or rear end edge of the sheet of paper collides with the nozzle surface and rubs against the nozzle surface. As a result, there is fear that the sheet of paper may be stained badly or the recording head may be damaged.
To solve this problem, for example, JP-A-Hei.5-77997 has disclosed the following technique. That is, suction ports are formed in a surface of the platen so as to communicate with a suction unit such as a suction fan. A current of air is generated so that the sheet of paper is sucked onto the surface of the platen to thereby prevent the sheet of paper from coming into contact with the nozzle surface.